Recently, as an information recording medium suited for distribution and long-term storage of a large amount of data, an optical disc has attracted attention. As a recording format for recording the data on the optical disc, there are known: (1) a read-only type in which embossed pits are formed in a recording layer by stamping in manufacturing and only the embossed pits can be reproduced; (2) a write-once type in which a recording film including pigment or the like is used for the recording layer and recording can be performed only once; (3) a rewritable type in which a magneto-optical recording film or a phase change recording film is used for the recording layer and data can be rewritten and deleted many times; and the like.
In order to respond to a requirement to increase a capacity of the optical disc as described above, there has been suggested an optical disc with a plurality of recording layers laminated. Conventionally, in the multilayer optical disc, the plurality of recording layers correspond to a single recording format. Each recording layer has a physical structure according to the recording format, and the recording layers share a logical structure according to the recording format.
Now, as an example of the shared logical structure, an explanation will be given to an area structure and assignment of a sector number in an optical disc of a dual-layer opposite track path type. Firstly, in a first recording layer (i.e. L0 layer), there are provided a lead-in area, a data area, and a middle area from an inner circumferential side to an outer circumferential side, and the sector number in a recording area of the optical disc increases from the inner circumferential side to the outer circumferential side. On the other hand, in a second recording layer (i.e. L1 layer), there are provided a middle area, a data area, and a lead-out area from the outer circumferential side to the inner circumferential side, and the sector number in the recording area of the optical disc, which is continued from a turn-around point in the L0 layer, increases from the outer circumferential side to the inner circumferential side. As described above, even in the case of the optical disc having the plurality of recording layers, if each recording layer corresponds to the same recording format, the optical disc is constructed from one type of the logical address.
An optical disc apparatus for performing the recording or reproduction on the optical disc detects a data recording position or reproduction position with reference to the sector number assigned in each data area and a recording layer number for specifying each recording layer.